Solar-thermal receiver systems rapidly lose pressure and temperature upon shutdown due to thermal losses at various components. Superheaters of a solar-thermal receiver are typically directly connected to the evaporator section of the receiver. Therefore, when the receiver is shut down, the steam volume present in the superheater condenses due to a heat transfer to the ambient. Accordingly, pressure in the superheater typically drops, and these pressure drops result in a steam flow into the superheater. This steam flow condenses until pressure reaches ambient. Condensed water in the superheater is typically drained, and accordingly its work potential is wasted. That is, since the condensed water in the superheater is drained and is wasted, operation of the receiver can result in wastage of high quality, chemically treated water. Furthermore, the pressure and temperature losses prolong or otherwise delay the start of an efficient use of the receiver startup time.
Once the receiver is shut down in the evening, it starts to lose pressure and temperature due to thermal losses at various receiver components. FIG. 1 depicts components 100 of a solar thermal receiver assembly. The superheaters 110 of the receiver may be directly connected, e.g., via a fluid conduit 115, to the evaporator section 120 of the receiver. When the receiver is shut down at the end of a cycle, or when the vertical separator pressure reaches ambient, the drum or vertical separator temperature of the day, steam volume present in the superheater section 110 condenses due to heat transfer to the ambient via convection, radiation, and conduction losses. When steam condenses in the superheater, e.g., in the superheater tubes 112, the pressure in the superheater may drop, resulting in steam flow from the drum 122 into the superheater 110. This direction of steam flow acts to lower the pressure in the drum 122 or vertical separator. In turn, this lowering of pressure causes the saturated water to flash in the drum 122 of the evaporator—so as to maintain equilibrium. The steam that entered the superheater 110 from the drum 122 condenses again, and the process continues until the pressure in the drum 122, or vertical separator, reaches ambient. Once the drum 122, or vertical separator, reaches ambient, the temperature of the drum 122, or vertical separator, continues to decline—but at a much slower rate than before reaching ambient. This change in the rate of decline may primarily be due to conductive heat loss from the insulation on the drum 122, or vertical separator, and downcomers 124.